CAREER: Confluence of magnetic and electric dipoles on the pyrochlore lattice

Part 1: Non-Technical Summary Materials that can respond to external stimuli (such as magnetic or electrical fields) are highly desirable for a wide variety of technological applications, including those relevant to the electronics and energy industries. While many materials have the ability to respond and interact with one type of external stimulus, only a few materials are known that can simultaneously interact with more than one stimulus and the discovery and understanding of such materials is an active area of research. With this CAREER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, Prof. Laurita’s group at Bates College focuses on understanding how the arrangement of atoms allows for interaction with external stimuli in a widely studied yet poorly understood family of materials called pyrochlores. The understanding and principles obtained from this work will ultimately offer design considerations for a broad range of technologically important properties. Undergraduate education and research are central to this work, which addresses a national need to educate and train future generations of material scientists. The proposed educational component establishes a bridge between graduate studies at research-intensive institutions and a career in undergraduate education at a primarily undergraduate institution (PUI). Through targeted advertisement at URM-serving graduate institutions, the principal investigator promotes participation of individuals from historically excluded and underrepresented groups. This program additionally plays a role in long-term and broader goals to diversify academic faculty, particularly at PUIs. With support from this grant hands-on, immersive internship experience at a research-focused PUI for upper-level graduate students will be created. This activity informs graduate students on a career at a PUI, provides valuable interaction and co-mentoring between graduate and undergraduate participants, and advances the science objectives of the grant and the graduate students’ dissertation work through collaborative research efforts. Part 2: Technical Summary The pyrochlore crystal structure exhibits a myriad of technologically relevant properties including superconductivity, ferroelectricity, photocatalysis, and frustrated magnetism. While there exists a wealth of studies on pyrochlores, the intricacies of this system leave many questions about intentionally manipulating the chemistry and structure for the desired functionality. The pyrochlore structure is inherently complex due to two interpenetrating subnetworks, and structural changes can be driven by substitution or vacancies on either network. Additionally, the triangular arrangement of cations on each sublattice leads to structural and behavioral questions due to geometrical constraints. The research carried out under this CAREER award builds on previous studies on the drivers of structural distortions in pyrochlores. Now the principal investigator investigates two hypotheses that arose from this work: (1) magnetic cations, regardless of long-range ordering, play a role in magnetoelectric interactions on both a local and crystallographic scale and (2) the crystallographic ordering of vacancies/dopants dictates the ordering of electric dipoles and is key to driving long range polar structures. The current work focuses on the confluence of magnetic and electric dipoles in the pyrochlore structure and the role of vacancies in these interactions. Specifically, the research investigates: (1) substitution of cations with the propensity to form electric dipoles (d0 or s2 electronic configurations), (2) substitution of magnetic cations with unpaired d or f electrons, and (3) the presence of anion vacancies; and thereby aims to contribute to our understanding of the complex structural behavior of pyrochlores, our understanding of the behavior and interaction of magnetic and electric dipoles on both a local and crystallographic scale, and ultimately towards the design of novel materials for multiferroic applications. With support from this grant hands-on, immersive internship experience at a research-focused PUI for upper-level graduate students will be created. This activity informs graduate students on a career at a PUI, provides valuable interaction and co-mentoring between graduate and undergraduate participants, and advances the science objectives of the grant and the graduate students’ dissertation work through collaborative research efforts. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.